1. Field of the Invention
This invention relates to methods and apparatus for quantifying components in liquid samples. The methods and apparatus of the present invention may be broadly applied for use in quantifying components in various liquid samples, and may be more specifically applied for use in the counting of white blood cells.
2. Description of the Prior Art
Quantification of components in liquid samples is a necessary procedure in many scientific fields. In medical diagnoses, quantification of components in various body fluids is often a useful tool. For example, the counting of white blood cells or red blood cells in a patient's blood can indicate various diseases or infections which the patient may have contracted. Quantification is also involved in the counting of spermatazoa in semen.
Various methods and equipment are known in the art for quantifying components in liquid samples. State of the art electronic equipment, such as the "Coulter Counter" (registered trademark of Coulter Electronics, Inc.), can be used for this purpose. However, such equipment can be very expensive, costing on the order of several thousands of dollars, upwards to tens of thousands of dollars. Thus, this option is often not available to hospitals and laboratories having low budgets, as is often the case in poorer or less developed countries than the United States.
Another method of quantifying components in liquid samples involves physically counting the components under a microscope in a known volume of the liquid sample. The volume is typically determined by multiplying the viewing area of the microscope by the thickness of the counting chamber. Various liquid sample holders have been designed for such purpose and are constructed so as to provide chambers of known and exact thickness. This has been achieved, for example, by precision grinding and cutting of glass, or the use of molded plastics, as disclosed in U.S. Pat. No. 4,501,496. Another counting chamber uses accurately drawn wire spacers which are permanently bonded between two sheets of glass, as disclosed in U.S. Pat. No. 3,198,064.
However, there are several disadvantages associated with the devices known in the prior art. First, the manufacturing cost involved is relatively high resulting in a high price to the consumer. Second, if it is necessary to mix the sample with a diluent before counting components in the sample, various other equipment must also be used. For example, before counting white blood cells in a blood sample, the red blood cells must typically be lysed by a hemolysing solution. (By "hemolysing solution" is meant a reagent that will selectively lyse red blood cells but not white blood cells). With the devices known in the prior art, the hemolysing solution and blood must first be pipetted to accurately determine the volume of each and then mixed in a diluting chamber so that the percent volume of diluent and blood in the mixture is known. Only after this procedure is complete can the sample be applied to the counting chamber in order to quantify the white blood cells.
In medical procedures, there is a need for great care in handling blood samples and other body fluids containing various infectious agents such as hepatitis and AIDS viruses. Therefore, it is desirable to use laboratory disposables as much as possible. In the quantification of components in liquid samples, the exposure risk of the worker to viruses within the samples is high during handling of the samples and quantification of components within the samples. Thus, it would be a particular advantage in the field of quantification of components in liquid samples if the counting chambers used were so inexpensive that they could be discarded after use. However, because of the high costs in manufacturing the above-described counting chambers and their resulting high price, it is not economical to dispose of them after use.
Thus, it would be an advance in the art if a precision made, disposable counting chamber were developed.
It is accordingly an object of this invention to provide methods and apparatus for quantifying components in liquid samples which can overcome or reduce the disadvantages of the prior systems.